1. Field of the Invention
This invention relates to a coeliac cavity ultrasonic diagnosis apparatus which includes an ultrasonic oscillator that is, an ultrasonic signal transducer adapted to be inserted into a coeliac cavity to effect a sector scan of an ultrasonic beam to produce an ultrasonic image of internal tissues.
2. Description of the Prior Art
In clinics, usefulness of an ultrasonic diagnosis apparatus which makes use of an ultrasonic wave has recently been noted. An ultrasonic diagnosis apparatus which can emit an ultrasonic pulse into a physical body from the surface thereof, receive a reflected wave from various organs with the body and observe movement of the abdomen, heart and embryo in real time and a coeliac cavity ultrasonic diagnosis apparatus which includes an ultrasonic oscillator adapted to be inserted into the rectum, for example, so as to examine the prostate gland have both been used in practice.
The coeliac cavity ultrasonic diagnosis apparatus permits use at a location more closely spaced from an organ of a living body and an ultrasonic wave having a frequency which is higher than that used in the former apparatus which emits ultrasonic pulses into the physical body from the surface thereof. Accordingly, it has an advantage that it is possible to obtain a picture image having a high resolving power.
The conventional coeliac cavity ultrasonic diagnosis apparatus heretofore proposed includes an insertable portion which is rigid in construction. The rigid insertable portion can be inserted into a relatively shallow coeliac cavity such, for example, as the rectum which is simple in configuration so as to effect diagnosis of the prostate gland. But, it has recently been desired to develope apparatus which makes the best use of the coeliac cavity ultrasonic diagnosis apparatus, and which has a flexible insertable portion such that the ultrasonic oscillator can be inserted into a coeliac cavity which is complex in configuration and of a substantial depth such as the esophagus or the stomach and which can examine organs such as the heart, pancreas or the like under a high resolving power.
In such coeliac cavity ultrasonic diagnosis apparatus, in order to obtain a sector scan image, since the insertable portion is limited in diameter, the insertable portion is provided at its distal end portion with an ultrasonic beam scanning means including an ultrasonic oscillator, and the rear end portion of the insertable portion is connected to an operating portion which is provided with a driving means for the ultrasonic beam scanning means, and an angle detector for detecting the direction of the ultrasonic beam or the like.
In the above mentioned coeliac cavity ultrasonic diagnosis apparatus including a rigid insertable portion, the ultrasonic beam scanning means provided at the distal end portion of the insertable portion is connected through a rigid shaft to the driving means and an angle detector provided at the operating member. In this case, the direction of the ultrasonic beam corresponds to the rotation of the angle detector with a ratio of 1:1, so that use may effectivey be made of a sin, cos function generation type potentiometer which has heretofore been used as the angle detector.
But, when the insertable portion is flexible, the ultrasonic beam scanning means must be connected through a flexible power transmission member such, for example, as a coil wire to the driving means and angle detector. In this case, the direction detected by the angle detector deviates from the practical direction of the ultrasonic beam due to a play involved in the torsional direction of the coil wire, and as a result, a desirous image can not precisely be displayed on a cathode ray tube. In addition, it is extremely difficult to correct such deviation.
In order to solve such a problem, it has heretofore been proposed to rotate the driving means such as a motor or the like at a constant speed, maintain a constant amount of deviation between the direction of the ultrasonic beam and the direction detected by the angle detector and correct the amount of deviation beforehand at the angle detector side.
But, if the distal end portion of the insertable portion is flexible as in the case of a flexible endoscope, the amount of deviation produced due to the play involved in the torsional direction of the coil wire changes in accordance with the inclined angle of the distal end portion of the insertable portion. As a result, it is not proper to use as the angle detector a sin, cos function generation type potentiometer operative to detect an absolute value of the angle.
In an ultrasonic diagnosis apparatus inclusive of a coeliac cavity ultrasonic diagnosis apparatus and operative to effect a sector scan or radial scan of an ultrasonic beam for the purpose of displaying an ultrasonic image on a cathode ray tube, if use is made of a sin, cos function generation type potentiometer as an angle detection means of the ultrasonic beam, emission of ultrasonic pulses and scanning on the cathode ray tube are effected by a selfscanning system and the ultrasonic beam is scanned automatically or manually.
In the case of automatically scanning the ultrasonic beam, the driving means such as a motor or the like causes the ultrasonic beam to rotate at a constant speed, so that a deflecting angle of the ultrasonic beam may easily be synchronized with the space between successive emissions of the ultrasonic beam. As a result, it is possible to make the density of the scanning lines on the cathode ray tube constant. But, in the case of manually scanning the ultrasonic beam, it is almost impossible to synchronize the deflecting angle of the ultrasonic beam with the space between successive emissions of the ultrasonic beam, and hence to linearly change the deflecting angle for the cathode ray tube. Thus, the density of the scanning lines on the cathode ray tube is not constant, producing blurs.
In addition, in the above mentioned coeliac cavity ultrasonic diagnosis apparatus which can obtain the sector scan image, it has been proposed to rotate an ultrasonic oscillator per se as the ultrasonic beam scanning means. In this case, however, when the ultrasonic oscillator per se is rotated, its lead wire is twisted and it tends to be easily damaged. Particularly, when the ultrasonic oscillator is surrounded by an ultrasonic wave transmission medium such as water or the like, there is also a risk of the lead wire thus damaged being shortcircuited through water.